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Both cinder and glance are starting to share the same logic for there engine notification listener, so instead of having them copy around that code it will be much nicer if taskflow can just provide itself a more capable listener that both can share and use directly. This avoids users of taskflow having to understand more about the internals of taskflow and its associated state then they likely need to understand (which makes taskflow easier to use and less work to integrate). Relevant locations where this already exists: - https://github.com/openstack/cinder/blob/master/cinder/flow_utils.py - https://review.openstack.org/#/c/85211/ Change-Id: I98eeb180b31bd488ae0eadd730e1530d7bae1f1f